Golf clubs, fishing rods and even utility poles are being made from resinous material incorporating a fiber, or fibrous, reinforcement--more specifically, such goods are being made from liquid, thermosetting resins incorporating roving, fabrics or matted materials as the reinforcement. Goods made from fiber reinforced resin material are, appropriately, designated as FRP members, and one of the principle ways in which FRP members are made is by helically winding a succession of resin impregnated reinforcing strands about a mandrel.
According to prior art techniques, one or more strands, or ribbons, of the reinforcing material is wound onto the mandrel, beginning at a first end thereof, in a helical configuration of one hand, and one or more successive strands, or ribbons, is wound, beginning at the second end thereof, onto the mandrel in a helical configuration of opposite hand. These steps are thereafter repeated with successive strands being wound adjacent the previous winding of like hand until the mandrel is completely covered and the desired thickness is acquired. Thereafter the member is cured.
By employing a successive series of wraps at opposite hand each reinforcing strand after the first lay is crimped as it accommodates to each crossover of previously laid strands. This crimping induces a stress concentration at the crossover when the finished product is stressed and also creates a small interstice where only the resin exists. Overall, this arrangement cannot, therefore, achieve the desideratum in mechanical properties which should be available from the material employed.
In addition, winding of the reinforcing strands has heretofore been accomplished by the use of winding heads that move at a constant rate along the mandrel as the latter rotates at a constant rate. Accordingly, if the mandrel tapers, say from the butt to the tip, the lead angle of the helical wrap will progressively increase from the butt to the tip. As the lead angle increases, the orientation of the reinforcing wrap changes to increase the flexural resistance provided by the reinforcing material. For many applications, such as with fishing poles, it is highly undesirable to increase flexural resistance in the tip portion of the rod.
Moreover, when the lead angle increases the torsional resistance decreases, and for many applications, notably as with golf club shafts, it is highly undesirable to decrease torsional resistance in the tip portion.
It must be appreciated that the FRP members to which the subject invention is directed are those which include reinforcing filaments disposed in an expanded helix and not those in which the filaments are all wound in a tight spiral where each wrap of a reinforcing filament engages the previous wrap of that same filament. Nor is the subject invention directed to FRP members in which the reinforcing filaments are either all longitudinally for a configuration of reinforcing filaments that are disposed in part longitudinally and in part in the aforesaid tight spiral.